function* gen() {
  console.log("start");
  let a = yield 1;
  console.log("a", a);
  let b = yield 2;
  console.log("b", b);
  let c = yield 3;
  console.log("c", c);
}
let it = gen();
let r1 = it.next();
console.log("r1", r1);
let r2 = it.next("a的值");
console.log("r2", r2);
let r3 = it.next("b的值");
console.log("r3", r3);

// it.next() 的值 是 yield 后面跟着的值 1;

//  a 的值 要通过 it.next("a的值") 传， a 值 为 'a的值'
